1. Technical Field
The present invention relates to a nickel bright-plated battery.
2. Related Art
In recent years, battery-powered apparatuses needing a large electric current such as digital still cameras have increased in number. Accordingly, high capacity dry batteries for a heavy load (discharging a large electric current) such as nickel-hydrogen batteries are beginning to be provided.
For example., the electromotive force of dry batteries such as LR is at a low voltage of about 1.5V. In order to draw a large current out of the low-voltage battery efficiently, electrical connection between the battery and a load (apparatus) needs to be kept good and stable over a long period of time. The battery is usually loaded into a battery holder (battery case) with spring contact terminals to be used. In this case, it is necessary to render the contact between the terminals of the battery and the terminals of the battery holder especially good and stable.
Hence, a nickel-plated steel plate is used as the terminal on the battery side. Furthermore, in order to make the appearance of batteries as products good, conventionally, steel plates having a bright (mirror) finish as their surface finish thereon are nickel bright-plated as shown in FIG. 5 and used.
FIG. 5 is a sectional view of a conventional battery and enlarged partial views of its terminals. The battery shown in the Figure has electricity generating elements including a solid cathode mixture 21, a separator 22 permeated by an electrolytic solution, and a gel-like anode mixture 23 put into a bottomed cylindrical battery can 11b, and the cathode can 11b is closed and sealed by an anode terminal plate 31b and a gasket 35.
The cathode can 11b works also as a cathode collector, and on the underside thereof, a convex cathode terminal 12b is formed. An anode terminal plate 31b has an anode collector 25 welded to its inner surface (on the battery inside), and its outer surface center forms an anode terminal 32b. The cylinder side, the other part than the terminals 11b, 32b, is covered by a cladding material 15.
The cathode can 11b has a steel plate 111b and a plating portion 112b as shown in its enlarged partial view of the Figure. The steel plate 111b has a bright finish on its surface. The plating portion 112b is formed by nickel bright-plating provided on the bright-finished surface. By this means, the surface of the cathode terminal 12b takes on smooth mirror brilliance. Likewise, the anode terminal plate 31b is also formed of a steel plate 311b having a bright-finished surface and a nickel bright-plating portion 312b as shown in its enlarged partial view of the Figure. By this means, the anode terminal 32b takes on smooth mirror brilliance.
Since the terminals 12b, 32b have smooth mirror brilliance on their surface, the above conventional battery is good in terms of appearance as a product (design effect). However, when the battery is loaded into the battery holder of a heavy load apparatus such as a digital still camera for use, the following problem occurs.
That is, if the surface of the battery terminal 12b (32b) is smooth mirror brilliance finished, contact with a contact terminal on the apparatus side (battery holder side) is over the entire terminal surface of the terminal 12b (32b). Hence, contact pressure on the apparatus side is dispersed to be small. In the case of low voltage, if contact pressure is not sufficient, contact failure is likely to occur. In order to prevent this from occurring, there is needed a countermeasure on the apparatus side that can produce sufficient contact pressure, but this requires providing, for example, especially strong spring pressure, and thus the load on the apparatus side is large.
Accordingly, the present inventors examined the use of steel plates having a dull (coarse surface) finish as their surface finish thereon. See, e.g., Japanese Patent Application Laid-Open Publication No. H06-314563. When the surfaces of dull finished steel plates are nickel bright-plated, fine bumps and dips (of the micron order) can be formed on the terminal surface with little damage to the appearance as a product (design effect). By this means, although the area of contact with the contact terminal on the apparatus side becomes smaller, contact pressure is concentrated locally, thus producing reliable electrical contact even with low voltage.
FIGS. 4A, 4B schematically show the electrical contact state of the terminals for their surface states in enlarged view. As shown in FIG. 4B, as to the terminal 12b (32b) having a surface of smooth mirror brilliance, the contact pressure acting between it and the contact terminal 50 on the apparatus side is dispersed, and thus it is hard to obtain reliable electrical contact. On the other hand, as shown in FIG. 4A, with the terminal 12b (32b) having fine bumps and dips on its surface, the contact pressure is concentrated on the bumps of the bumps and dips, and thereby reliable electrical contact can be obtained even with low voltage.
However, the inventors found that even with the nickel bright-plated terminal surface having fine bumps and dips formed thereon as shown in FIG. 4A, the contact degrades during a long period of time and that such degradation in contact occurs as becomes a problem especially when drawing a large current. In this case, as a means to improve the contact, there is a method where the terminals are plated with a conductive material such as gold that is excellent in conductivity and chemical stability, but the problem occurs that cost increases.